Selenium rectifier



Sept. 14,1948. w. E. BLACKBURN 2,449,444

SELENIUM RECTIFIER Filed oct. so, 1946 Wag/)7e Blac L lm.

Patented Sept. 14, 1948 2,449,444 SELENIUM nac'rmm Wayne E. Blackburn. Wilkinsburg. Pa.,

to Westinghouse Electric Corporation.

assignor East Pittsburgh, Pa., a corporation oi' Pennsylvania. Application October 30, 1946, Serial No. 706,758

4 Claims. 1 My invention relates to selenium rectiflers and, in particular, relates to anV improved process for forming the blocking or barrier layer in such rectiers. In accordancewith the prior art. such barrier layers have been produced by exposing the free surface of the selenium to lthe vapors of certain materialswhile in vacuum, by chemically treating `the seleniumsurfacegand by depositing a film of organic material on the selenium surface by dipping in a suitable solution. I'he latter has, in general. been vi'ound to be the least Y expensive but difficulty arises because films of organic material are likely to` decompose at the temperatures at which the'rectiflers are heattreated during lsubsequent steps of the manufacturing process.. The barrier layer thereafter comprises some carbonaceous material of uncertain composition. Furthermore, if the rectlfier is subjected to high temperatures during the subsequent operation, for example, by reason of the heat generated by losses within the rectifier itself. further decomposition of the organic material in the barrier layer occurs. Thus the maximum temperature, and hence load output of which the rectifier is capable in use is limited because such subsequent decomposition produces changes in the rectifier characteristics which cannot be tolerated.

One object of my present invention is to produce a barrier layer on the selenium of selenium rectiflers by a dipping process which produces an inorganic film on the free surface of the selenium. v

Another object of my invention is to produce a selenium rectifier which is capable of'operating at higher temperatures than were selenium rectiflers of the prior art.

Anotherobject of my invention is'to produce .i

a selenium 'rectifier having more stable characteristics both electrically and chemically than did selenium rectiers of the prior art.

Other objects of my invention'will becomeapparent upon reading the following specification, taken in connection with the accompanying drawing, in which the single gure is a sectional view of a rectifier embodying the principles of my invention.

In the preferred embodiment of my invention,

Iproduce the inorganic barrier layer by coating the selenium surface with a solution or `suspension of a suitable inorganic salt in van organic liquid, and subsequently by driving olf the or- `ganic material before completion of the rectifier.

The preferred method ofmakixng this rectifier is .to first produce a coatingof amorphous sele- 2 nium on a. suitable base plate which may, for example, be sheet iron, sand blasted and nickel plated. Such a sheet iron base is selenium-coated by dipping the plate in a bath of the molten selenium and throwing on excess material through centrifugal force by rotating the plate after dipping. The base plate thus coated is then submerged in a hot solution or suspension of an inorganic salt-in an organic solvent., I have found that salts which are most effective are those whose metals form stabley oxides, suliides l or selenides.

As examples of the most suitable salts, I will mention uranium nitrate, zirconium nitrate, magnesiumthiosulfate, gallium nitrate, zinc dithionate, potassium columbate. aluminum ni#- trate and cerous nitrate. The most desirable organic solvent to be employed is alcohol or acetone. The density of the salt in the solution has not been found by my experiments to date to be critical but may, for example, be that correspondling tov saturation.

After withdrawal from the bath, the solvent soon evaporates leaving a coating of the dissolved salt on the surface `of the selenium. A coating, which may be cadmium or a cadmium alloy well known in the art, may then be metalsprayed onto the surface of this coating to form the counter-electrode. The unit thus produced is then submitted toa heat treatment compris-l ing annealing for a period ,of about minutes at a temperature of 200 degrees centigrade. This converts'the amorphous selenium into crystalline selenium and at the same time causes the deposited film to produce the desired barrier layer. Thereafter the rectifier is, in accordance with a method well known in the artl subjected to electrical forming by impressing upon it an alternating voltage :of 35 volts for a period of 60 minutes. The rectifier unit is then complete.

It is my Apresent belief that the deposited inorganic salt undergesdchemical combination with the selenium on which it is deposited to form a selenide, or possibly combines with oxygen of the air to some extent. Since the exact reaction is uncertain, I will hereinafter arbitrarily refer to the combination above described as an Oxy-salt of the metal.

Referring in detail to the drawing, a completed vrectifier thus comprises ay base plate I having on one surface a layer 2 of selenium, the free surface of the layer being covered'with a barrier layer 3 resulting from the deposition of the above-mentioned inorganic salt. The free 3 face ofv the barrier layer 3 is coated 'with a counter-electrode I as above described.

I claim as my invention: v

1. The method of producing a selenium rectiner which comprises the step of coating a .free

' surface of selenium with a. suspension of magneslum thiosulfate in s. volatile organic solvent.

2. The method o! producing a selenium rec-` tiiier which comprises ythe step of. coating the free surface of selenium with a solution of magnesium thlosulfate in alcohol.

3. The method of producing a selenium rectifier which comprises the step of coating the free `free surface of selenium with a solution of magnesium thiosulfate in acetone.

REFERENCES CITED The following references are of record in the file of this patent: Y

l UNITED STATES PATENTS Number Name Date 2,137,316A van Geel et al Nov. 22. 1938 2.189.731 Do Boer et al.y Dec. 13, 1938 De Boer et al. Sept. 19. 1939 

